For several years there has been an increasing demand for dependable pipeline closures in large sizes, in some cases even for pressures in excess of 1,000 pounds per square inch and temperatures as high as 1800.degree. F. One of the major industrial developments creating these new requirements is a nuclear energy powered electrical generating plant. Because of the enormous power available in nuclear energy, it is possible to construct a single generating plant which is many times the capacity of one of the older conventional plants. In addition, the normal hazards of plant operation are greatly increased in the nuclear power plant, because of the nature of the process and its control and the radiation effects of the materials and the process. These increased hazards have placed a greater importance upon the reliability of the hardware used in the plant.
The valve of the present invention embodies a valve operating mechanism which is fully enclosed within the primary pressure containment of the valve. This precludes any part of the operator being damaged by missiles resulting from other system failures. The energy source for the operator is the steam in the pipeline itself, providing assurance that any time energy is needed to close the valve, it is available and, should the steam pressure fail, the valve will close by itself. Control of the valve operator is performed from a remote site through an appropriate control system and with the system having a fail safe characteristic to allow the valve to close in an emergency.